[Integration of natural sciences and basic medical subjects in the integrated dentistry program (iMED DENT) at the University of Hamburg].

In October 2019, an integrated dentistry program (iMED DENT) was implemented at the University of Hamburg and was the first of its kind in Germany. This model curriculum builds on didactic concepts that have been applied successfully for many years in curricula for human medicine, including interdisciplinary teaching, early clinical experience, and scientific education. The first year focuses on the healthy situation ("normal function") and aims to integrate the natural sciences (biology, chemistry, physics) and the basic medical subjects (anatomy, biochemistry, physiology, medical terminology) in the context of dental health.

GPER1 deficiency causes sex-specific dysregulation of hippocampal plasticity and cognitive function.

Estrogens regulate synaptic properties and influence hippocampus-related learning and memory via estrogen receptors, which include the G-protein-coupled estrogen receptor 1 (GPER1). Studying mice, in which the GPER1 gene is dysfunctional (GPER1-KO), we here provide evidence for sex-specific roles of GPER1 in these processes. GPER1-KO males showed reduced anxiety in the elevated plus maze, whereas the fear response ('freezing') was specifically increased in GPER1-KO females in a contextual fear conditioning paradigm.

Sex-specific Regulation of Spine Density and Synaptic Proteins by G-protein-coupled Estrogen Receptor (GPER)1 in Developing Hippocampus.

G-protein-coupled-estrogen-receptor 1 (GPER1) is a membrane-bound receptor that mediates estrogen signaling via intracellular signaling cascades. We recently showed that GPER1 promotes the distal dendritic enrichment of hyperpolarization activated and cyclic nucleotide-gated (HCN)1 channels in CA1 stratum lacunosum-moleculare (SLM), suggesting a role of GPER1-mediated signaling in neuronal plasticity. Here we studied whether this role involves processes of structural plasticity, such as the regulation of spine and synapse density in SLM.

Distal Dendritic Enrichment of HCN1 Channels in Hippocampal CA1 Is Promoted by Estrogen, but Does Not Require Reelin.

HCN1 compartmentalization in CA1 pyramidal cells, essential for hippocampal information processing, is believed to be controlled by the extracellular matrix protein Reelin. Expression of Reelin, in turn, is stimulated by 17β-estradiol (E2). In this study, we therefore tested whether E2 regulates the compartmentalization of HCN1 in CA1 via Reelin.

Reelin and aromatase cooperate in ovarian follicle development.

Reelin plays an important role in cerebral cortex development and synaptogenesis. In the hippocampus, the neurosteroid estrogen affects reelin expression. In this study we tested a potential crosstalk between estradiol and reelin, thus the possibility of a reelin-induced activation of the estradiol synthesizing enzyme aromatase.

Sex-Dependent Regulation of Aromatase-Mediated Synaptic Plasticity in the Basolateral Amygdala.

The basolateral amygdala (BLA) integrates sensory input from cortical and subcortical regions, a function that requires marked synaptic plasticity. Here we provide evidence that cytochrome P450 aromatase (AROM), the enzyme converting testosterone to 17β-estradiol (E2), contributes to the regulation of this plasticity in a sex-specific manner. We show that AROM is expressed in the BLA, particularly in the basolateral nucleus (BL), in male and female rodents.

Nedd4-2 regulates surface expression and may affect N-glycosylation of hyperpolarization-activated cyclic nucleotide-gated (HCN)-1 channels.

HCN channels are important regulators of neuronal excitability. The proper function of these channels is governed by various mechanisms, including post-translational modifications of channel subunits. Here, we provide evidence that ubiquitination via a ubiquitin ligase, neuronal precursor cell expressed developmentally downregulated (Nedd)-4-2, is involved in the regulation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels.

HCN1 subunits contribute to the kinetics of I(h) in neonatal cortical plate neurons.

The distribution of ion channels in neurons regulates neuronal activity and proper formation of neuronal networks during neuronal development. One of the channels is the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel constituting the molecular substrate of hyperpolarization-activated current (I(h)). Our previous study implied a role for the fastest activating subunit HCN1 in the generation of Ih in rat neonatal cortical plate neurons.

ZD7288 enhances long-term depression at early postnatal medial perforant path-granule cell synapses.

Hyperpolarization-activated, cyclic nucleotide-gated nonselective (HCN) channels modulate both membrane potential and resistance and play a significant role in synaptic plasticity. We compared the influence of HCN channels on long-term depression (LTD) at the medial perforant path-granule cell synapse in early postnatal (P9-15) and adult (P30-60) rats. LTD was elicited in P9-15 slices using low-frequency stimulation (LFS, 900 pulses, 1 Hz; 80 ± 4% of baseline).

Aromatase inhibition abolishes LTP generation in female but not in male mice.

Inhibitors of aromatase, the final enzyme of estradiol synthesis, are suspected of inducing memory deficits in women. In previous experiments, we found hippocampal spine synapse loss in female mice that had been treated with letrozole, a potent aromatase inhibitor. In this study, we therefore focused on the effects of letrozole on long-term potentiation (LTP), which is an electrophysiological parameter of memory and is known to induce spines, and on phosphorylation of cofilin, which stabilizes the spine cytoskeleton and is required for LTP in mice.

Regulation of axonal HCN1 trafficking in perforant path involves expression of specific TRIP8b isoforms.

The functions of HCN channels in neurons depend critically on their subcellular localization, requiring fine-tuned machinery that regulates subcellular channel trafficking. Here we provide evidence that regulatory mechanisms governing axonal HCN channel trafficking involve association of the channels with specific isoforms of the auxiliary subunit TRIP8b. In the medial perforant path, which normally contains HCN1 channels in axon terminals in immature but not in adult rodents, we found axonal HCN1 significantly increased in adult mice lacking TRIP8b (TRIP8b(-/-)).

Upregulation of presynaptic mGluR2, but not mGluR3 in the epileptic medial perforant path.

Presynaptic metabotropic glutamate receptors (mGluRs) at glutamatergic synapses play a major role in governing release probability. Previous reports indicated a downregulation of group III mGluRs at the lateral perforant path-granule cell synapse in the chronically epileptic hippocampus. Here, we investigated the mGluR-dependent presynaptic inhibition at the medial perforant path-granule cell synapse in the pilocarpine-treated chronically epileptic rat.

The 27-kDa heat shock protein (HSP27) is a reliable hippocampal marker of full development of pilocarpine-induced status epilepticus.

Purpose: The pilocarpine-induced status epilepticus (SE) in rodents provides a valuable animal model of temporal lobe epilepsy. Since not all animals enter SE following pilocarpine injection, we aimed to find a biomarker for full development of pilocarpine-induced SE using a proteomic approach.

Methods: Two-dimensional gel electrophoresis and Western blot analysis were performed with protein extracts from hippocampal tissue taken from four different groups of animals: pilocarpine-treated rats with full development of SE, pilocarpine-treated rats without seizures, pilocarpine-treated rats with seizures but without SE, and saline-injected rats.

Deletion of the hyperpolarization-activated cyclic nucleotide-gated channel auxiliary subunit TRIP8b impairs hippocampal Ih localization and function and promotes antidepressant behavior in mice.

Output properties of neurons are greatly shaped by voltage-gated ion channels, whose biophysical properties and localization within axodendritic compartments serve to significantly transform the original input. The hyperpolarization-activated current, I(h), is mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and plays a fundamental role in influencing neuronal excitability by regulating both membrane potential and input resistance. In neurons such as cortical and hippocampal pyramidal neurons, the subcellular localization of HCN channels plays a critical functional role, yet mechanisms controlling HCN channel trafficking are not fully understood.

Roles of 17ß-estradiol involve regulation of reelin expression and synaptogenesis in the dentate gyrus.

Studies on the role of 17β-estradiol (E2) in the hippocampus have mainly focused on CA1 and CA3 regions, whereas in dentate gyrus (DG), its role is largely unknown. Here, we examined potential functions of E2 in DG, particularly during development. Immunohistochemistry and in situ hybridization revealed abundance of estrogen receptor (ER)α, but not ERβ, expression in DG.

HCN1 channels constrain DHPG-induced LTD at hippocampal Schaffer collateral-CA1 synapses.

HCN channels play a fundamental role in determining resting membrane potential and regulating synaptic function. Here, we investigated the involvement of HCN channels in basal synaptic transmission and long-term depression (LTD) at the Schaffer collateral-CA1 synapse. Bath application of the HCN channel blocker ZD7288 (10 microM) caused a significant increase in synaptic transmission that was due to an enhancement in AMPA receptor-mediated excitatory postsynaptic potentials.

Postnatal expression pattern of HCN channel isoforms in thalamic neurons: relationship to maturation of thalamocortical oscillations.

Hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels are the molecular substrate of the hyperpolarization-activated inward current (I(h)). Because the developmental profile of HCN channels in the thalamus is not well understood, we combined electrophysiological, molecular, immunohistochemical, EEG recordings in vivo, and computer modeling techniques to examine HCN gene expression and I(h) properties in rat thalamocortical relay (TC) neurons in the dorsal part of the lateral geniculate nucleus and the functional consequence of this maturation. Recordings of TC neurons revealed an approximate sixfold increase in I(h) density between postnatal day 3 (P3) and P106, which was accompanied by significantly altered current kinetics, cAMP sensitivity, and steady-state activation properties.

Hyperpolarization activated cyclic-nucleotide gated (HCN) channels in developing neuronal networks.

Developing neuronal networks evolve continuously, requiring that neurons modulate both their intrinsic properties and their responses to incoming synaptic signals. Emerging evidence supports roles for the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in this neuronal plasticity. HCN channels seem particularly suited for fine-tuning neuronal properties and responses because of their remarkably large and variable repertoire of functions, enabling integration of a wide range of cellular signals.

Activity-dependent heteromerization of the hyperpolarization-activated, cyclic-nucleotide gated (HCN) channels: role of N-linked glycosylation.

Formation of heteromeric complexes of ion channels via co-assembly of different subunit isoforms provides an important mechanism for enhanced channel diversity. We have previously demonstrated co-association of the hyperpolarization activated cyclic-nucleotide gated (HCN1/HCN2) channel isoforms that was regulated by network (seizure) activity in developing hippocampus. However, the mechanisms that underlie this augmented expression of heteromeric complexes have remained unknown.

Mechanisms of seizure-induced 'transcriptional channelopathy' of hyperpolarization-activated cyclic nucleotide gated (HCN) channels.

Epilepsy may result from abnormal function of ion channels, such as those caused by genetic mutations. Recently, pathological alterations of the expression or localization of normal channels have been implicated in epilepsy generation, and termed 'acquired channelopathies'. Altered expression levels of the HCN channels - that conduct the hyperpolarization-activated current, I(h) - have been demonstrated in hippocampus of patients with severe temporal lobe epilepsy as well as in animal models of temporal lobe and absence epilepsies.

Epileptogenesis in the developing brain: what can we learn from animal models?

Knowledge of the processes by which epilepsy is generated (epileptogenesis) is incomplete and has been a topic of major research efforts. Animal models can inform us about these processes. We focus on the distinguishing features of epileptogenesis in the developing brain and model prolonged febrile seizures (FS) that are associated with human temporal lobe epilepsy.

Localization of HCN1 channels to presynaptic compartments: novel plasticity that may contribute to hippocampal maturation.

Increasing evidence supports roles for the current mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, I(h), in hippocampal maturation and specifically in the evolving changes of intrinsic properties as well as network responses of hippocampal neurons. Here, we describe a novel developmental plasticity of HCN channel expression in axonal and presynaptic compartments: HCN1 channels were localized to axon terminals of the perforant path (the major hippocampal afferent pathway) of immature rats, where they modulated synaptic efficacy. However, presynaptic expression and functions of the channels disappeared with maturation.

Regulated expression of HCN channels and cAMP levels shape the properties of the h current in developing rat hippocampus.

The hyperpolarization-activated current (I(h)) contributes to intrinsic properties and network responses of neurons. Its biophysical properties depend on the expression profiles of the underlying hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels and the presence of cyclic AMP (cAMP) that potently and differentially modulates I(h) conducted by HCN1, HCN2 and/or HCN4. Here, we studied the properties of I(h) in hippocampal CA1 pyramidal cells, the developmental evolution of the HCN-subunit isoforms that contribute to this current, and their interplay with age-dependent free cAMP concentrations, using electrophysiological, molecular and biochemical methods.

Quantitative analysis and subcellular distribution of mRNA and protein expression of the hyperpolarization-activated cyclic nucleotide-gated channels throughout development in rat hippocampus.

The properties of the hyperpolarization-activated current (I(h)) and its roles in hippocampal network function evolve radically during development. Because I(h) is conducted by the hyperpolarization-activated cyclic nucleotide-gated (HCN) cation channels, we tested the hypothesis that understanding the quantitative developmental profiles of HCN1, HCN2, and HCN4 expression, and the isoform- and age-specific progression of their subcellular distribution, should shed light on the established modifications of the properties of I(h) throughout development. Combined quantitative in situ hybridization, regional western blots, and high-resolution, dual-label immunocytochemistry revealed striking and novel information about the expression and distribution of the HCN channel isoforms in the developing hippocampal formation.